Three-dimensional digital subtraction rotation angiography (3D DSA rotation angiography) is a standard method for assessing the vascular anatomy before and during interventions. In digital subtraction angiography (DSA), mask images (images without contrast agent) and fill images (images with contrast agent) are first generated and then subtracted from one another so that only the changes over time induced by the contrast agent and reproducing the vessels are obtained.
Such a C-arm X-ray system for digital subtraction angiography, as shown by way of example in FIG. 1, has for example a C-arm 2 which is rotatably mounted on a stand in the form of a six-axis industrial or articulated arm robot 1 and at the ends of which are mounted an X-ray radiation source, for example an X-ray tube assembly 3 with X-ray tube and collimator, and an X-ray image detector 4 as image recording unit.
The articulated arm robot 1 known for example from U.S. Pat. No. 7,500,784 B2, which preferably has six axes of rotation and hence six degrees of freedom, enables the C-arm 2 to be moved to an arbitrary position in space, for example by being rotated around a center of rotation between the X-ray tube assembly 3 and the X-ray detector 4. The inventive X-ray system 1 to 4 can be rotated in particular around centers of rotation and axes of rotation in the C-arm plane of the X-ray image detector 4, preferably around the center point of the X-ray image detector 4 and around axes of rotation intersecting the center point of the X-ray image detector 4.
The known articulated arm robot 1 has a base frame which is permanently installed on a floor for example. Attached thereto is a carousel which is rotatable about a first axis of rotation. Mounted on the carousel so as to be pivotable about a second axis of rotation is a robot rocker arm to which is attached a robot arm which is rotatable about a third axis of rotation. Mounted on the end of the robot arm is a robot hand which is rotatable about a fourth axis of rotation. The robot hand has a retaining element for the C-arm 2, said retaining element being pivotable about a fifth axis of rotation and rotatable about a sixth axis of rotation running perpendicular thereto.
The X-ray diagnostic apparatus is not dependent on the industrial robot in terms of its implementation. Conventional C-arm devices can also be used.
The X-ray image detector 4 can be a rectangular or square, flat semiconductor detector which is preferably produced from amorphous silicon (a-Si). Integrating and possibly counting CMOS detectors can also be used, however.
A patient 6 to be examined is placed as the examination subject in the beam path of the X-ray tube assembly 3 on a patient positioning table 5 so that images of the heart, for example, can be recorded. Connected to the X-ray diagnostic apparatus is a system control unit 7 having an image system 8 which receives and processes the image signals from the X-ray image detector 4 (control elements are not shown, for example). The X-ray images can then be viewed on a monitor 9.
In neuroradiology in particular, three-dimensional digital subtraction angiography (3D DSA) is a routine tool for planning and performing minimally invasive procedures. Modern neurological operating rooms also integrate this 3D capability with a rotating C-arm in order to enable pre- and intra-procedural 3D imaging of the cerebral blood vessels.
Two C-arms are widely used in neuroradiology. These are what are known as biplane systems, as described in more detail with reference to FIG. 2 as a typical interventional suite with patient table. Said systems essentially have two so-called planes, wherein the first plane 10 can consist of the X-ray diagnostic apparatus shown in FIG. 1, comprising C-arm 2, X-ray tube assembly 3 and X-ray image detector 4. A ceiling-suspended C-arm 2′ having an X-ray tube assembly 3′ and an X-ray image detector 4′ of a second plane 12 can be provided via a ceiling fixture 11. A suspended monitor array 13 having a first display 14 for the first plane 10 and a second display 15 for the second plane 12 can also be mounted on the ceiling. A high-voltage generator 16 is provided in addition to the system control unit 7.
During an operation the brain tissue and the cerebral vessels, in particular the parts close to the surface, may be displaced after the cranium is opened.
In order to achieve a refreshed rendering of the situation it is customary in neurosurgery to perform a fluorescence angiography, an ICG angiography for example. ICG, indocyanine green, is a fluorescent dye which is employed in medicine as an optical contrast agent. In such applications it can be injected intravenously into the surface vessels. In order to fluoresce ICG is excited by means of a light source, as described for example in the dissertation at the Faculty of Medicine of the Ludwig Maximilian University in Munich titled “Validierung der Fluoreszenz-Angiographie zur intraoperativen Beurteilung and Quantifizierung der Myokardperfusion” (“Validation of fluorescence angiography for intraoperative assessment and quantification of myocardial perfusion”) by Sabine Helena Wipper, 2006. Due to the limited penetration depth of red and infrared light only the surface structures can be reproduced by these and other optical methods.